Drive



A ril 14, 1964 D. v. BENNETT ETAL 3,129,365

' DRIVE Filed Aug. 50. 1960 7 Sheets-Sheet 1 Fig. I r r3 rl r3 L8 I 0R3 I l PGI WITNESSES INVENTORS /& Donald V. Bennett, Sylvester J. Campbell 8| AIbertB$ Oglesby p 1964 D. v. BENNETT ETAL 3,129,365

DRIVE Filed Aug. 50, 1960 '7 Sheets-Sheet 4 R GRI WB GS2 I I I I I I I I l l I I I I I I I I I I I l I I I I I l l I April 14, 1964 v, BENNETT ETAL 3,129,365

' DRIVE Filed Aug. 30, 1960 7 Sheets-Sheet 5 i I20 A I 60 HP u II I I i April 1 1964 D. v. BENNETT ETAL 3,129,365

DRIVE Filed 30, 1960 7 sheets-sheet 6 ill I l 2.0. V5.0. 2.0. 2

AAAALA llAlA l n n Y' '7 I IV V5.0. 2 J1. 1 lO/25JL 65/I60n I lllll l I I I 50 HP I I l I I IOOO/3500n. I

IAAAA I 3,129,365 DRIVE Donald V. Bennett, Tonawanda, N.Y., and Sylvester J. ampbeil, Penn Hills, and Albert G. Oglesby, Gibsonia, Pa, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Filed Aug. 30, 1960, Ser. No. 52,924 2 Claims. (Cl. 1318-16) This invention relates to the art of electric drives; and has particular relationship to a drive for a web such as pulp. or semi-finished paper being processed in. a paper mill. Typically this invention concerns itself with a drive for advancing a web through a calender dryer having a plurality of rolls. The web is advanced from an output or first calendar to the calender dryer and from the calender dryer to an input or secondcalender. The calender dryer, the input calender and the output calender are separately driven and the drives are adjustable so that the web may be tensioned either between the input calender and the dryer or between the dryer and the output calender. Usually the drives of the first and second calenders deliver substantially greater power than the drive of the calender dryer. Typically, the first and second calenders may have drives capable of delivering 400 horsepower while the. calender dryer may have a 40 horsepower drive. Where tension is applied, to the Web as it is moving between the. calender dryer and the second calender the second calender may be driven at a higher speed than the first calender. Under such circumstances, the motor of the calender dryer drive operates regeneratively. Where the tension is to. be applied to the part of the web between the first calender and, the dryer the motor is supplied with power and the drive may be described as operating. generatively.

Because of the driving interconnection between the first and second calenders and the calender dryer and because the calender dryer drive is of relatively low power, it is desirable that the calender dryer drive. be prevented from being excessively loaded during normal operation. This object is achieved by setting the speed control of the calender dryer so that the power supplied to the drive is below that at which full speed would be produced. In addition, current limiting facilities arev provided which limit the loading of the. drive during normal operation generally to the rating of the calender dryer drive. Typically, the current limit facilities may permit adjustment of the loading of the calender dryer drive to between 30% and 110% of rated loading.

In apparatus in accordance with the teachings of the prior art, the current limit is set generally to limit the loading of the calender dryer drive motor to rated load ing throughout the whole operation of the apparatus, both during normal running process and during the threading process. The apparatus is threaded both at the start of an operation and also on the occurrence of a break in the web. During the threading, the. speed of the calender dryer motor'is adjusted in accordance with the teachings of the art by a resistor which is usually referred to as the Draw Adjust rheostat. Typically, on the average about three breaks per day occur and following each break it is necessary in accordance with the teachings of the prior art to. rethread the web using the Draw Adjust rheostat to bring the calender dryer motor up to speed.

In the use of the prior art apparatus, it was found that the calender dryer motor consumes a relatively long time in coming up to speed. Typically, the interval so consumed is of the order of about four minutes. Apparatus of the type described here treats web at the rate or about 1000 feet per minute; delay of 4 minutes per break or 12 minutes per day results in a loss of United States Patent 6 12,000 feet of the paperproduct per day. In a typical. situation the width of the paper. may be inches or roughly 8 feet, Twelve minutes shut-down time would, then result in a lossot 96,000 feet. The paper produced may weigh about 3 6 pounds per 3000 square feet. The. loss" from shut-down time would then amount to, about 1290 pounds, At 50 cents per. .pound loss amounts to $600 per day or $180,000 for a 300 day year. i

It is then an objeet of this invention to reduce the loss arising from. the shut-down time following a break in, th b d ri Prot st g A more specific objectof this inventi n is to reduce the time taken for web treating apparatus as disclosed herein to reach, normal. operating speed following shut: down occasioned by a break in the web,

A more specific object of this invention is to provide a novel drive for a calender dryer, the use of which shall reduce the time. required to bring the drive up to normal operating speed following a break in the web.

Another specific object of invention is toprovide a novel magnetic-a mphfier control circuit having general utility but particularly useful in. accelerating the motor of a. calender dryer to normal operating speed following a break.

The calender dryer motor of web processing apparatus is controlled by a device such as a saturable reactor which responds to the. relationship between the motor speed and the shaft of the input calender to synchronize the operation of -:the. motor and the input calender. Typically, the reactor may control the field of a generator which supplies the motor. This control system is provided with current-limit means which limits the current supplied to the motor so as to prevent excessive overloading of the motor. The, synchronization is elfected in dependence upon. a signal which is generally equal to a function of the difierence between a potential dependent on the speed at which the web is being advanced into the calender drive and a potential dependent on the speed of the motor. The current limit is effected by comparing the current load of the motor with a set potential and. impressing a current-limit control signal to reduce sharply the supply of power to the motor when the current loading exceeds a predetermined magnitude.

In accordance wih this invention, the reference signal during threading is set at a magnitude higher than the magnitude. during normal generative operation so as to condition the motor to reach operating speed at a high rate and at the same time the current limit is set to permit substantial overloading of the motor. Typically, the current limit may be set to permit the motor to operate at 200% of rated load. This setting of the. reference signal and the current limit during threading conditions allows calender dryer drive to reach operating speed rapidly. It has been found in operation of apparatus in the practice of this invention that following a break in the web the calender dryer drive reaches operating speed in a time interval of the order of one minute. Thus nine minutes per day are saved in shut-down time following breaks. This saving amounts to A of the $180,000 per year lost in shut-down time or about $135,000 per year for each calender dryer unit of the apparatus.

In the preferred practice ofthis invention, both the ref-.

erence signal supply circuit and the current limit circuit are maintained permanently set for threading. The transition from the threading setting to the normal operating setting is elfected by a relay which responds to a change in loading of the motor automatically to reset the apparatus for threading. i

' The novel features considered characteristic of this invention are disclosed generally above. A clearer understanding of this invention both as to its organization and as to its method of operation, together with addi- '3 tional objects and advantages thereof will be derived from the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic view showing a web processing system in which this invention is incorporated;

FIGS. 2A, 2B and 2C together constitute a schematic of a preferred embodiment of this invention;

FIGS. 3A, 3B and 3C together constitute a schematic similar to FIGS. 2A, 2B, 2C, but showing the magnitudes and the types of the components of apparatus in accordance with this invention which was constructed and found to operate satisfactorily; and

FIGS. 3A and 3B are included herein only for the purpose of aiding those skilled in the art in practicing this invention and not wtih any intention'of in any respect limiting the scope thereof.

The magnitudes of the resistances of the various adjustable or variable resistors in FIGS. 3A, 3B, 3C are represented as a number followed by a slant line followed by a larger number. The number to the left of the slant line indicates the setting of the corresponding resistor. Thus in actual practice, resistor 14R is set at 3000 ohms, resistor 15R1 at 2800 ohms, resistor 15R2 at 3750 ohms and resistor 7R at 40 ohms (FIG. 3C).

FIGURE 1 shows the portion of a web processing system in which this invention is incorporated. The overall apparatus may' include a number of such systems. The apparatus shown in FIG. 1 includes an input or first calender C1, an output or second calender C3 and a calender dryer DC interposed between the calenders C1 and C2. The calender C1 includes a plurality of rolls r 1 and Drl through which the web W is passed. Certain of the rolls are driven by a drive (not shown). The line shaft LS connected by drive roll Dr1 which advances the web W from the calender C1 is coupled through an alternating-current pilot generator PG1. PG1 produces an alternating current dependent on the speed of this shaft LS. The amplitude of this alternating current is proportional to the speed of roll Drl and this in turn is proportional to the speed of the web. The alternating current produced by PG1 is used in synchronizing the movement of the web as it leaves calender C1 with its movement to the other portions of the apparatus.

The output calender C3 also includes a plurality of rolls r3 and D16 over which the web is advanced after it leaves the calender dryer DC. The calender C3 may transmit the web W to additional processing apparatus and may be synchronized with the latter. 7

The calender dryer DC includes a plurality of rolls r2 which are driven from a direct-current motor M1. The motor is energized from a generator G which in turn is driven by a three-phase motor MD energized from the supply. (See FIGS. 2A-2B.) The motor M1 also. drives an alternating-current pilot generator RG2 which produces an alternating potential, the amplitude of which is dependent, preferably. proportional to, the speed of the motor M1. PG2 cooperates with PG1 to provide a reference signal maintained for roper synchronism of the drives for web W.

The drives for calenders C1 and C3 are of very high power. The drive for the dryer calender DC is of relatively low power of the order of of either of the drives C1 or C3. In the "usual practice of this invention the calender C3 may be driven at a somewhat higher speed than the calender C1 and the web between C3 and DC is under tension. Under such circumstances the Web in the calender dryer DC drives the motor M1 and the latter operates regeneratively supplying power to the generator G rather than absorbing power from the generator.

In the event of a break in the web at a point X for example, the drive of the calender dryer DC would assume the full load of advancing the web W from calender C1 through the calender dryer DC. The power required to advance the web is high compared with the power rating of the drive GM1. Typically, the drive G M1 4 may have a rating of 40 horsepower and the demand on GM1 to advance the web W from the calender C1 to the calender dryer DC without the aid of C3 may be controlled in dependence upon the relationship between the drive GM1 the power supplied to the generator G is of the order of 350 horsepower. To prevent damage to the potentials from PG1 and PG2 so as to' prevent the drive DC from attempting to operate at a high speed and in addition a current-limit control is introduced which prevents overloading of the generator G.

Specifically, the apparatus in accordance with this invention includes a DRIVE and a CONTROL (see FIGS. 2A, 2B, 2C). The division of the apparatus in this way is on a functional and not a structural basis. The DRIVE andthe CONTROL may be subdivided into components in separate cabinets which may be disposed in diiferent parts of the installation. For example, there'may be parts at the operators station, near calender C1, near calender C3 or near the calender dryer.

This apparatus is supplied from the conductors L1, L2, L3 which may be connected to the buses of a three-phase supply through the usual disconnects or circuit breakers (not shown). The controlling components of the DRIVE and the CONTROL are supplied from direct-current conductors P and N which may be energized from conductors L1 and L3 through contacts lMa and 1M0 through a transformer AT and a rectifier IRX. The potential for the current-limit control is derived from conductors L1, L2, L3 through the contacts lMa, lMb, 1M0 of contactor 1M and rectifier SRX which is energized by the secondary AS1 of the transformer ATl. Single-phase alternating current for control purposes is derived from conductors AL1 and ALZ energized from conductors L1 and L3 through contacts lMa and lMc through a constant-potential transformer KT which may, for example, be a SOLA transformer.

The DRIVE includes a main generator G, a motor M for driving the generator and the drive motor M1 which drives the rolls r2 of the calender dryer DC. The motor M is adapted to be supplied from the conductors L1, L2 and L3 through the contacts lMiz, lMb, 1M0 of the contactor 1M. The coil of the contactor 1M is adapted to be connected between conductors L1 and L3 through a normally closed stop push-button SP and a normally open start push-button ST and to be locked in through its front contact 1Md.

The generator G has a commutating field winding PC, a series field winding FS, a shunt field winding GF and a differential shunt field winding GFD. The motor Ml has a commutating field winding FCl, a series field winding PS1 and a shunt field winding MIF; The generator G is adapted to be connected in power interchanged relationship with the motor M1 through the commutating winding PC, the series field winding FS, a low resistor 3R, the series field winding 'FSI, the commutating winding FCl and a contact Ma of a contactor M in the CON- TROL. V

'The generator G may operate generatively to supply motoring power to the motor M1 in situations where the motor M1 is being brought'up to starting speed or to operating speed. The generator G and the motor M1 may also operate regeneratively in which case the motor M1 supplies power to the generator G.

In accordance with the specific aspects of this invention, provisions are included for producing a response to a change in the current flow either from the generator G to the motor M1 or from the motor M1 to the generator G on the occurrence of such an event as a break in the web. These provisions include relays AAV and DAV in the CONTROL. The relay DAV responds in situations in which the motor M1 is feeding power to the generator G, the relay AAV responds in situations in which the generator G is feeding power to the motor M1. The coil of relay DAV is 'adapted to be connected across the windings PC, PS and FSland the resistor 3R through a rectifier ZRX and the front contact REVa of the reverse relay REV which is actuated when the operation is regenerative from the motor Ml to the generator G. The coil of AAV is adapted to be connected similarly through the rectifier ERX and the contact FWDa when the operation is generative and the flow of power is from the generator G to the motor M1.

The control of current through the main shunt field winding GF of the generator G is controlled by magnetic amplifier MA. This amplifier has an output winding W0, a bias winding WB, an inching winding WI, a voltage control winding WV, damping windings WD and WDl, current limit windings WCL, reference Winding WR and speed winding WS. The field winding GF is supplied from conductors ALT and ALZ through the winding W0 and through the rectifier 4RX connected in the usual rectifying relationship with the winding W0.

There is a dot adjacent each winding to show the effect on the output through W0 of ampere turns through the winding. Positive current flowing from the dot through the winding tends to increase the output through W0 and positive current flowing through the winding to the dot tends to decrease the output through W0. Thus an increase in ampere turns through winding WR results in an increase in the ampere turns through W0 and a decrease results in a decrease in the ampere turns through W0. The main shunt field GP of the generator G varies with the output of W0 so that an increase in the output through W0 produces an increase in the field and a decrease through W0 produces a decrease in this main shunt field. Under the influence of GFD the potential of G would be opposite to that shown in FIG. 2A. An increase in this potential would result in an increase in the ampere turns through WV which would result in an increase in the ampere turns through WV, and an increase in the current through GF. This would tend to counteract the current through GED and reduce the opposite potential.

The bias winding WE is supplied from conductors P and N through a filtering capacitor 10. The capacitor is. charged by the potential drop across a variable resistor 3RH which is connected in series with a resistor 7R between P and N. The charging circuit for the capacitor includes a resistor 6R. The bias winding WB is connected across the capacitor through resistor 6R1. Inching winding W1 is similarly supplied from a filtering capacitor 2C across which it is connected through a resistor 8R1. The filtering capacitor is adapted to be charged from conductors P and N through a front contact INCa of arelay INC in the CONTROL and a resistor 9R and a variable resistor dRH. The charging circuit for the capacitor 20 includes the resistor 8R. The voltage compensation winding WV is connected across the armature of the generator G and the field windings FC and PS through a back contact of contactor M in the CONTROL, a variable resistor 11R, and a fixed resistor 12R. The voltage winding WV operates to assure that the generator voltage is zero when. the equipment is not in operation and the generator G is deenergized. Even a small voltage on the generator G would produce a surge through the contactor Mn when this contactor is closed. The voltage winding WV is also adapted to be connected across the armature of generator G, the field winding FC and the field winding PS through the inching contactor lNCb and through a resistor ltiRH. The function of the winding WV in this case is to counteract the effect of the differential winding GFD so that the inching may be precise.

The damping windings WD and WDl are supplied from a variable resistor SRl-l connected across the armature of the generator G to field winding FC and the field winding PS, the windings WD and WDl are connected in series to the arm of the resistor SRH through a fixed resistor 13R and a capacitor 30. The resistor 13R and the capacitor 3C operate to differentiate the potential derived from SRH.

The current-limit winding WCL is supplied from the rectifier SRX and the circuit through which it is supplied incorporates important features of this invention in its specific aspects. This. circuit includes the resistors 21R1, ZtlRI-I, 21R, llRH, ZRH, 22R, 22RH and MR1 connected in series across the rectifier SRX. These resistors operate to set the blocking potential derived from the rectifier SRX which determines the voltage for which load reducing current starts to flow through the current-limit winding WCL. The selected voltage provided by this bank of resistors is balanced against the voltage derived across resistor 3R which carries the current flowing between the generator G and the motor M1. One terminal of this resistor is connected to the junction J3 of the resistors lRI-l and ZRH and the other terminal of this resistor 3R is connected through the resistor 6RH and the winding WCL to the junction I which, in turn, is connected to the bank of resistors through rectifiers 6RX and 7RX. The rectifiers fiRX and 7RX are oppositely poled, 6RX conducting under the potential across the resistor 3R is produced; by generative operation when the generator G is feeding the motor M1 and the other 7RX conducting during regenerative operation when the motor M1 is feeding the generator G.

The resistors 22R, 22RH and 22R1 are during standby and during the threading operation shunted by forward relay back contact FWDb. Similarly, the resistors 21R1, ZQRH and 21R are shunted by REVb during threading or standby. During threading or standby, the resistors IRH, and ZRH are then effective. The adjustable arm of lRH is connected to J2 through back contact REVd; the adjustable arm of ZRH is connected to J1 through back contact FWDd. During standby and threading, the arm of ZRH is electrically negative by a relatively high potential with respect to point J3. to which the resistor 3R is connected. Current is conducted through WCL only if the potential across 3R resulting from the supply of current from generator G to motor M1 is greater than this potential between. ZRH and J3. This. means that current limit is not applied until the current through SR is substantial. For example, if the arm of ZRH is at minus 10 volts relative to J3, current only flows through WCL if the drop across 3R is more than 10 volts with t1 electrically positive relative to t2. The flow of the current through WCL would reduce the output of generator G. The same relationship exists with respect to the potential between the adjustable arm of IRH and J3. In this case again the regenerative current through 3R from 22 to t1 must produce a drop higher than the drop between the arm of IRH and J3 before the currentlimit winding WCL conducts current. In this case, the current through WCL increases the output of G to reduce the regenerative effect.

The point It is also adapted to be connected to the arm of variable resistor ZZRH through front contact FWDe.

The potential impressed from rectifier SRX at J1 or 12 when contacts REVe or FWDe respectively are closed and contacts REVd or FWDd are open is substantially smaller than the potential impressed through IRH or ZRH when REVd and FWDd are closed and REVe and FWDe are open. A smaller potential then across resistor 3R in either case permits current to flow through the current-limit winding WCL. Usually the resistors IRE-I or ZRH are set so that the current limit winding.

WCL is supplied with current when the flow through resistor 3R corresponds to about 200% of rated loading of the motor M1. The resistors ZORH and ZZRH are usually operated over the range from 30% rated. loading of the motor M1 to rated loading.

Windings WR and. WS cooperate to, maintain the first calender and the calender dryer drive in proper synchronism. Winding WR is supplied from the. pilot generator PGl through rectifier 7RX and winding WS is supplied from pilot generator PGZ through rectifier ttRX. The

potential delivered by PGZ corresponds to the actual speed of the motor MI and the potential delivered by PGl corresponds to the speed of the line shaft or the speed at which the input calender C1 is supplying the web W. The ampere turns through WR are counteracted on the ampere turns through WS.

The potential of rectifier 8RX is impressed across WS through a filter, a fixed resistor 18R and an adjustable resistor 7RH. The filter includes capacitors 4C and 5C which are connected to the positive terminal of 8RX through resistors 19R and 26R respectively. A rheostat 24RH serving for metering purposes is connected across.

. winding WR through a circuit which constitutes an important feature of this invention in its specific aspects. This circuit includes the resistors 14R, 23RH, R1 and 15R2 which are connected in series. In standby or threading operation, resistors 14R and ZtiRI-I are effective, resistances 15R1 and ISRZ being shunted by contact FWDh or REVh. During generative operation resistor 15111 is elfective and during regenerative operation the resistor IESRZ is effective. The efiects of these variable resistors in the different modes of operation can be understood by a consideration of FIGURE 3C in which the magnitudes of the various resistances are presented.

During threading, the ampere turns through WR are higher than in the regenerative setting during running, and lower than in the generative setting during running. The motor then has the highest speed in the regenerative setting during running, next highest in the threading setting and the lowest in the generative setting during running.

The CONTROL includes in addition to the contactors M, 1M, 1NC and the relays REV, FWD, DAV and AAV, the contactors 2M and 3M and the relays ACR and VR. The coil of contactor 2M is adapted to be connected between conductors P and N through back contact VRa, a contact APXa of a photoelectric relay (not shown) which closes if the ventilation is adequate, a start push-button ST1 which is normally open, a normally closed stop pushbutton SP1 and a front contact ACRa of the relay ACR. Contactor 2M is adapted to be locked in through its own front contact ZMa. During inching the coil of the inching contactor INC is adapted to be connected between conductors P and N through contacts VRa, APXa, inch pushbutton IC, 2M1), and ACRb. This coil of contactor, INC is adapted to be locked in through its contact INCc. The coil contactor M is adapted to be connected between conductors P and N through front contact 2M6 and to be locked in through contacts VRb, ACRe, and Mb, and alternatively through INCd. The coil of contactor 3M is adapted to be connected between conductors P and N through front contact 2M0.

When the apparatusis to be set for regenerative operation the load limit reverse push-button RS is closed and the coil of relay REV is adapted to be connected between conductors P and N through front contact 3Ma, normally closed push button RT, push button RS and interlock contact FWD The coil of REV is adapted to be locked in through DAVa if the voltage impressed across DAV is of appropriate magnitude. When the apparatus is to operate generatively the load-limit forward push-button PD is closed and the coil of the relay FWD is connected between conductors P and N through contact 3Ma, normally closed push-button RT, push-button FD, interlock contact REV This coil is locked in through contact AAVa of relay AAV if the voltage across the generator and motor is appropriate. The coil of relay ACR is connected between conductors ALI and ALZ and this relay is actuated if there is potential between AL1 and AL2. The coil of relay VR is connected i is actuated closing contacts ACRa, ACRh, ACRc.

acrossthe armature of motor M1 and the field windings FCll and PS1 and thisrrelay is actuated if the potential across the armature of the motor M1 is of appropriate magnitude; that is, if the speed of the motor is above a predetermined magnitude. Relay VR remains unactuated at inching speeds.

During standby, the conductors L1, L2 and L3 are energized by the closing of the disconnects or circuit breakers (not shown). Start button ST is then closed energizing contactor 1M and locking this contactor in.

7 pere turns through these windings is determined by the biasing ampere turns through WB and the ampere turns through WV and contact Md. These ampere turns are so set that the differential field GFD is counteracted and the potential of generator G is substantially zero. There is no current through the winding WR during standby because the contactor 3M is open and there is no current through WS during standby because the motor M1 is deenergized at Ma and the generator PGZ produces no potential. The motor Ml'being deenergized, relay VR is deenergized. Relays AAV and DAV are deenergized. Since P and N are energized the fields of PGI and P62 and the field GFD are energized.

Preliminary to the threading operation it may be desirable to inch the apparatus for various purposes. To accomplish this object theinch-button IC 'is closed, this picks up the inch relay INC and it is locked in across VRa and APXa through the inch contact INCc. INCd closes picking up contactor M, this connects generator G to motor M1 through contact Ma. In addition, Md is opened and the contact INCb is closed to set the voltage winding WV for inching. INCa is also closed to supply pattern current through the winding WI permitting the motor to operate at inching speed. The effect of the pattern winding WI is to set the motor M1 ata low speed. The ampere turns through Winding WV regulates the voltage of the generator G during the inching. The speed of the motor M1 is not adequate to pickup VR.

In the standby condition, the start button ST1 is open, contactor 2M is deenergized, contactor M is then deenergized, contactor 3M is deenergized, and relays REV and FWD are deenergized. The inching button IC is also open so that the inching contactor INC is deenergized. The contactor M being deenergized, contact Ma is open and the generator G and motor M1 are disconnected. Contact Md is closed so that there is current through winding WV. This current is of such polarity as to reduce the voltage of generator G to'zero. The

inch contacts INCa and INCb are both open so that there.

is no pattern ampere turns through the winding WI. The inch button IC is usually operated repeatedly until the desired inching operation is completed.

The apparatus is now ready for threading and is set with relays REV and FWD unactuated so that the back potential blocking the current flow through winding WCL is high. The motor M1 is then conditioned to draw substantial overload current. In addition, the circuit which supplies current through WR is set for threading and the resistor ZSRH is set for the desired threading speed. This resistor remains in this position throughout the operation of the apparatus. 7

It may now be assumed that the apparatusis to be set in operation that the first calender C1 isin operation.

feeding web W towards the calender dryer DC. The second calender C2 may also be assumed to be in operation. Since the first calender C1 is in operation the generator P61 is supplying potential dependent on the speed at which the web W is being fed towards the calender dryer but no ampere turns flow through WR since at this point contact -3Mb is open. The motor M1 is at this point also deenergized and no potential is supplied by PG2.

To carry out the threading operation, the start pushbutton ST1 is closed; this energizes contactor 2M which is locked in by its contact ZMa. energizing contactor M, contact ZMd is closed energiz ing contactor 3M. Contac'tor 3M0: is closed condition ing the load limit reverse and load limit forward circuits to be actuated.

The actuation of contactor M closes contact Ma connecting the generator G and the motor M1 in power interchange relationship. Md is opened deenergizing the voltage winding WV. SMb closes energizing WR from the generator PGl. At this point, the reference circuit is set with the resistances 14R and 28RH controlling the current through the reference winding. Excitation of the generator is now increased and the potential supplied by the generator G to the motor M1 increases bringing the motor M1 up to speed. The reference ampere turns through WR is balanced against the speed ampere turns through WS produced by the pilot generator PG2 so that the generator voltage is essentially proportional to the net signal derived from the reference and speed windings. The operator may adjust the rheostat 28RH to vary the reference signal so as to match the speed of the motor M1 with the speed at which the web is being supplied. Once the proper threading speed is attained the precise speed match of the motor M1 and the calender C1 is achieved and the rheostat 28RH may remain set so that on the return to any threading operation following a break the precise threading speed is achieved. With the relays FWD and REV deenergized the current limit circuit is set to permit substantial overload during the threading operation. The threading operation may be interrupted if necessary by opening the stop button SP1.

When the motor M1 reaches substantial speed the relay VR is actuated locking in the contactor M through VRb, ACRe, Mb. The push-button ST1 is released once the desired speed is achieved and if the motor voltage drops for any reason the contact VRb opens deenergizing the contactor M and opening the motor supply circuit.

Once the web W is threaded through the apparatus it is necessary to set the apparatus into normal running operation. The apparatus may be set in two Ways. The web between the calender dryer DC and the calender C3 may be tensioned and the web between the calender C1 and the calender dryer DC may be in a loop or the web between the calender dryer DC and the calender C3 may be in a loop and the web between the calender C1 and the calender dryer DC may be tensioned. The first mode of operation is achieved by setting the apparatus to operate regeneratively, that is with the motor M1 supplying the generator G. This object is accom plished by closing the reverse push-button RS. Relay REV is then actuated closing contact REVa and connecting the coil of relay DAV between the motor M1 and the generator G. In addition, REVh opens connecting resistor 15R2 in circuit with WR and REVg closes short circuiting resistors 4R and ZSRH. WR is now supplied with lower current than during threading since 15R2 is greater than 4R and ZSRH (see FIGS. 3A and 3B). The power output of the generator is then decreased and since the counter electromotive force of the motor M1 is not changed the motor regenerates. The regenerative current causes relay DAV to be energized through rectifier ZRX, this locks in relay REV and the push-button RS may be released. In addition, the actuation of REV closes contact REVe and opens contact REVd setting the current limit for substantially lower loading than it is set during threading. The current limit may be adjusted by setting the rheostat 20RH. If it is desired that the web be in a loop between C3 and DC and tight between C1 and DC Contact ZMc is closed the apparatus is set for generative operation by closing push-button FD. This actuates relay FWD connecting AAV across the generator G and the motor M1 and also setting the reference circuit with 15R1 controlling the ampere turns through WR. 15121 is smaller than 4R and ZSRI-I (see FIG. 3C) permitting larger current to flow thruogh WR and-increasing the potential of the generator G so that it feeds the motor M1. The speed of the motor M1 then increases slightly applying tension to the web between calender C1 and the calender dryer DC and producing a slight loop in the web between the dryer DC and the calender C3. In this case, the forward portion of the current limit circuit is set for controlling the current limit by the opening of contact FWDd and the closing of contact FWDe. Relay AAV is in this case actuated locking in the relay FWD so long as the current flowing through the field windings PC, PS and PS1 remains adequate;

The opening of load limit reset button RT deenergizes the relays REV and FWD and reverts the apparatus to the threading setting.

On the occurrence of a break in the web the speed of motor M1 decreases substantially causing either DAV or AAV, as the case may be, to drop out. This deenergizes the relay REV or FWD as the case may be and sets the apparatus for threading so that the reference ampere turns through WR is now controlled by resistors 4R and ZSRH and the current limit by either resistor IRH or resistor 2RH depending on the character of the operation. At the new setting the apparatus is set precisely for threading since the resistor ZSRH is in the setting where it was left after the initial threading operation. The currentlimit circuit is now set to permit substantial overload so that the generator G is driven in such a way that the motor M1 reaches the threading speed in a very short time of the order of a minute and the apparatus may be quickly reset for continued operation.

While a preferred embodiment of this invention has been disclosed herein, many modifications thereof are feasible. This invention then is not to be restricted except insofar as is necessitated by the spirit of the prior art.

The claims are:

1. Control apparatus including a motor, a generator, means connected to said generator for connecting said motor and generator in power-interchange relationship, means connected to said motor for deriving from said motor a potential dependent on the speed of said motor, means connected to said generator for deriving a potential dependent on the loading of said generator by said motor, magnetic amplifier means including output Winding means, current-limit winding means, and reference winding means, the ampere turns through said reference winding means controlling the ampere turns through said output winding means, and ampere turns through said current-limit winding means varying the ampere turns through said output winding means so as to reduce the loading of said motor on said generator, current supply means for supplying a reference potential having alternatively a first magnitude for producing generative operation of said motor and generator, a second magnitude for producing regenerative operation of said motor and generator and a third magnitude intermediate said first and second magnitudes for accelerating said motor, means connecting said reference potential and said speed responsive potential in balancing relationship to said reference winding means, additional current supply means for supplying a blocking potential having alternatively a first magnitude corresponding to generative operation of said motor and generator, a second magnitude corresponding to regenerative operation of said motor and generator, and a third potential having an absolute magnitude substantially higher than said last-named first and second magnitudes corresponding to operation of said motor and generator in accelerating said motor, and means connecting said loading dependent potential in overriding rela- 1 1 tionship with said blocking potential to said current-limit Winding means.

2. A drive for Web treating apparatus including a calender dryer and means coupled to said web for advancing said Web to said dryer, said drive comprising a motor, a generator, means connected to said generator for connecting said motor and generator in power-interchange relationship, means connected to said motor for deriving from said motor a potential dependent on the speed of said motor, means connected to said generator for deriving a potential dependent on the loading of said generator by said motor, magnetic amplifier means including output Winding means, current-limit winding means, and speed comparing Winding means, the ampere turns through said speed comparing Winding means controlling the ampere turns through said output Winding means, and ampere turns through said current-limit Winding means varying the ampere turns through said output winding means so as to reduce the loading of said motor on said generator, means responsive to said web advancing means for supplying a reference potential having alternatively a first magnitude for producing generative operation of said motor and generator, a second magnitude for producing regenerative operation of said motor and generator and a third magnitude intermediate said first and second magnitudes for accelerating said motor, means connecting said reference potential and said motor References Cited in the file of this patent UNITED STATES PATENTS 2,399,059 Pell Apr. 23, 1946 2,601,957 Halter July 1, 1952 2,684,458' Winchester July 20, 1954 2,709,772 Fisher et a1 May 31, 1955 2,749,493 Fischer June 5, 1956 2,845,586 Stringer July 29, 1958 3,061,534 Jasperson Oct. 30, 1962 3,073,996 Bacheler et al. Jan. 15, 1963 FOREIGN PATENTS 1,079,174 Germany' Apr. 7, 1960 

1. CONTROL APPARATUS INCLUDING A MOTOR, A GENERATOR, MEANS CONNECTED TO SAID GENERATOR FOR DERIVING A POTENTIAL DEPENDENT ON THE LOADING OF SAID GENERATOR BY SAID MOTOR, MAGNETIC AMPLIFIER MEANS INCLUDING OUTPUT WINDING MEANS, CURRENT-LIMIT WINDING MEANS, AND REFERENCE WINDING MEANS, THE AMPERE TURNS THROUGH SAID REFERENCE WINDING MEANS CONTROLLING THE AMPERE TURNS THROUGH SAID OUTPUT WINDING MEANS, AND AMPERE TURNS THROUGH SAID CURRENT-LIMIT WINDING MEANS VARYING THE AMPERE TURNS THROUGH SAID OUTPUT WINDING MEANS SO AS TO REDUCE THE LOADING OF SAID MOTOR ON SAID GENERATOR, CURRENT SUPPLY MEANS FOR SUPPLYING A REFERENCE POTENTIAL HAVING ALTERNATTIVELY A FIRST MAGNITUDE FOR PRODUCING GENERATIVE OPERATION OF SAID MOTOR AND GENERATOR, A SECOND MAGNITUDE FOR PRODUCING REGENERATIVE OPERATION OF SAID MOTOR AND GENERATOR AND A THIRD MAGNITUDE INTERMEDIATE SAID FIRST AND SECOND MAGNITUDES FOR ACCELERATING SAID MOTOR, MEANS CONNECTING SAID REFERENCE POTENTIAL AND SAID SPEED RESPONSIVE POTENTIAL IN BALANCING RELATIONSHIP TO SAID REFERENCE WINDING MEANS, ADDITIONAL CURRENT SUPPLY MEANS FOR SUPPLYING A BLOCKING POTENTIAL HAVING ALTERNATIVELY A FIRST MAGNITUDE CORRESPONDING TO GENERATIVE OPERATION OF SAID MOTOR AND GENERATOR, A SECOND MAGNITUDE CORRESPONDING TO REGENERATIVE OPERATION OF SAID MOTOR AND GENERATOR, AND A THIRD POTENTIAL HAVING AN ABSOLUTE MAGNITUDE SUBSTANTIALLY HIGHER THAN SAID LAST-NAMED FIRST AND SECOND MAGNITUDES CORRESPONDING TO OPERATION OF SAID MOTOR AND GENERATOR IN ACCELERATING SAID MOTOR, AND MEANS CONNECTING SAID LOADING DEPENDENT POTENTIAL IN OVERRIDING RELATIONSHIP WITH SAID BLOCKING POTENTIAL TO SAID CURRENT-LIMIT WINDING MEANS. 